NEW YORK • When North Korea tested a missile that fell harmlessly into the sea this month, it was more than just an attempt by its 33-year-old leader, Mr Kim Jong Un, to jolt a new US President.
Arms experts observed something new: solid-fuel technology that makes such missiles easier to hide and launch quickly.
North Korea's nuclear weapons programme has progressed in four areas that bear watching: arsenal size, bomb strength, missile technology and ability to elude detection.
1. ARSENAL SIZE
Small, but thought to be growing
Experts estimate that North Korea has fewer than 10 nuclear weapons. By one estimate, the country now has enough plutonium and highly enriched uranium to build 20 to 25 nuclear weapons.
2. EXPLOSIVE POWER
From 1 kilotonne to 10 kilotonnes in 10 years
The explosive force of North Korea's first nuclear device, tested in October 2006, was less than a kilotonne, which is equivalent to 1,000 tonnes of TNT.
Its second test, in 2008, had more than double that force.
Seismic readings of North Korea's fifth test in September last year, however, registered a force of about 10 kilotonnes, according to South Korea's Defence Ministry.
Missiles could reach contiguous
US by 2026 In 1999, Mr George Tenet, then director of the CIA, said he could hardly overstate his concern about North Korea's programme, warning that the Taepodong-1 missile, with a reach of up to 2,000km, could deliver bomb payloads to Alaska and Hawaii.
In the nearly two decades since, the country's investment in becoming a nuclear weapons power has succeeded despite diplomacy and international sanctions.
Last year, North Korea conducted dozens of missile tests. Some missiles could be launched from mobile pads and submarines, making them easier to hide.
4. COVERT CAPABILITY
Smaller, more mobile weapons
In August last year, North Korea test-fired a ballistic missile from a submarine, demonstrating a significant improvement in its ability to strike enemies stealthily.
Solid-fuel rockets, like the new Pukguksong-2 test-fired last Sunday, can be stored on mobile launchers, rolled out and prepared for launch in minutes.
The North said the test was conducted from a self-propelled mobile launcher. "All of these factors would make it much harder to find and pre-emptively destroy the Pukguksong-2," missile expert John Schilling wrote on 38 North website.